Oil well drilling fluid



Patented Dec. 7, 1943 on. WELL DRILLING FLUID John W. Freeland, SanFrancisco, and Harold T.

Byck, Berkeley, Calif., assignors to Shell Development Company, SanFrancisco, Calif., a. corporation of Delaware No Drawing. ApplicationJune 22, 1940, Serial No. 341,964

\ 8 Claims. (01. 252-85) This invention pertains to improvements in oilwell drilling fluids and relates more particularly to an improveddrilling fluid containing Irish moss as a plastering or protectiveagent.

This application is a continuation-in-part of our copending application,Serial No. 283,970, filed July 12, 1939, now Patent No. 2,211,688, datedAug. 13, 1940.

The functions of a drilling fluid are to lubricate and cool the bit, tocarry the cuttings from the bit to the surface, to control formationpressures, and to form on the walls of the borehole a thin,

adherent, impermeable sheath capable of preventing or minimizing thepenetration of the drilling fluid into the formation, and its losstherein.

As the drilling fluid is circulated in the borehole under a pressureexceeding that of the formation, its liquid component, together with thesmaller colloidal or solid particles suspended therein, flows into theformation through the interstices, passages and pores between the grainsof the formation sands. The larger clay or solid particles, however,become arrested between adjacent sand grains and act as plugs,decreasing the area of the flow passages therebetween, and allowingsmaller clay particles to become in turn arrested and to act as plugs insaid smaller passages. In the plugging of these smaller pores, thethixotropic structure developed by the drillerties of the drilling fluidmay be brought about by the natural salinity of the brlnes encounteredor by the penetration of salt domes by the drill where the solution ofthe formation quickly flocculates the drilling fluid, or by thenecessity, for wantof fresh water, of using sea water or other lowquality water in making up the fluid. The plastering properties ofdrilling fluids are likewise impaired by increased temperature of thedrilling fluid due to its contact with subsurface strata at elevatedtemperature and its absorption of the heat generated by the bit inpenetrating the rock, which is one of the functions of a drilling fluid.This temperature increase causes temperature flocculation of thecolloidal particles, flocculation due to increased solubility offlocculating salts, and accelerated flocculation ing fluid serves as asupport or mesh on which the smaller clay particles build. A drillingfluid of good plastering properties quickly forms in this manner asubstantially liquid-impervious mud sheath on the walls of the borehole.

Unfortunately, however, these properties, commonly referred to asplastering properties, are particularly sensitive to certain types ofcontamination frequently encountered during drilling, namely,contamination with salts capable of causing a partial or completeflocculation of the clay colloids of the drilling fluid. Theflocculation of the clay colloids, that is, the agglomeration andaggregation of the small colloidal particles into larger non-colloidalparticles, precludes the formation of a thixotropic structure by thedrilling fluid and/or the plugging of the smaller pores or passages inthe walls of the borehole and thus leads to a great loss of water orliquid from the drilling fluid into the formation. For example, adrilling fluid under 500 lbs. pressure lost 25.5 cc. of water through aporous filter in thirty minutes; the same drilling fluid containing 10%common salt lost 54.0 cc. of water in the same time. This impairment ofthe plastering propby salts at elevated temperature as well as increasedfluidity of the liquid medium in the drilling fluid. For example, thepercentage increase in water loss from F. to F. for a group of sixCalifornia muds ranged from about 65% to 157%.

' It is therefore an object of the present invention to provide adrilling fluid of improved plastering properties, which is capable offorming a thin, adherent, and impermeable mud sheath on the walls of theborehole to prevent loss of fluid into the formation.

It is another object of the invention to provide a drilling fluid ofimproved plastering properties, which properties are substantiallyunaffected by salt contaminations, or by standing for considerableperiods of time.

It is still another object of this invention to provide a drilling fluidof improved plastering properties, which may be prepared with salt wateras the liquid component.

It is a further object of the invention to provide a drilling fluid ofimproved plastering properties, which properties are not greatlyaffected by high well temperatures.

Another object of this invention is to provide a method of attaining theabove objects by means of a small amount of a material, which isinexpensive, non-corrosive, non-poisonous, and nonvolatile.

Briefly, the method of the present invention comprises dispersing in thedrilling fluid a small amount of Irish moss obtained by drying theseaweed C'hondrus crispus.

While it has already been known to add to drilling fluids varioussubstances extracted, leached, or chemically prepared from seaweedssuch, for example, as alginates, agar-agar, etc.,

the use of Irish moss offers the following advantages over the use ofthese agents; first, Irish moss may be used in its natural or driedform, and is therefore economically more attractive than said extracts,the costly chemical processes of preparation being dispensed with; andsecond, the Irish moss used in its natural form is more effective thanthe concentrated extracts from other seaweeds hitherto used for the samepurpose, as will be shown hereinbelow.

In applying the process of the present invention during drilling of awell for the purpose of forming a mud sheath of particular strength onthe walls of the borehole to prevent the escape of gases and to avoidthe infiltration of water into the well or a loss of the circulationfluid into porous formations, and particularly in the event where thedrilling fluid is liable to be contaminated by salts or subjected toincreased temperatures, an aqueous dispersion of Irish moss containingin suspension materials such as clay, shale, limestone and/or, ifdesired, suitably ground weighting material such as barytes, galena,iron or lead oxide, oyster shells, etc., may be used for forming thedrilling fluid alone or in combination, if desired, with a compound ormixture of compounds known as viscosity reducers, such as thewater-soluble salts of organic materials of feebly-acidic propertiessuch as tannins, humins, lignins, extracts of wood, such as quebrachoextract, etc., in admixture with alkali hydroxides, the water-solublealkali metal pyrophosphates, meta-phosphates, hexa-phosphates,polyphosphates, etc. In general, the use of a mixture of a material suchas quebracho extract and sodium hydroxide, which is commercially knownas quebracho-soda, is preferred. As will be shown hereinbelow, theobject of adding these agents is not to reduce the viscosity of thedrilling fluid but to enhance the action of the Irish moss in combatingthe effects of salt contamination, high temperatures, etc. Suspensionscontaining from about 0.1% to 1.0%, and preferably about 0.6%, of Irishmoss may be used, depending on the quality of improvement desired, andthe amount, type and particle size of the suspended material. While 0.6%is the optimum concentration for Irish moss, considerably lowerconcentrations, such as 0.1% to 0.2%, suifice in certain cases toprotect the mud against salt 4 contamination.

The improved drilling fluids of the present invention may be prepared,preferably, by using an aqueous dispersion of Irish moss as part orwhole of the liquid component in making up a mud with clay and othermaterials, or dry Irish moss may be incorporated in a prepared mud byviolent agitation. It is preferable that Irish moss be dispersed as aprotective agent in the drilling fluid prior to salt contamination sincebetter results are obtained in this manner. For example, the water losswas 3.9 cc. at 45 minutes for a mud sample to which Irish.moss and thensalt was added, while for a mud sample to which the salt was added firstthe water loss amounted to 6.9 cc. in the same time. In locations wherefresh water is unavailable, salt water, such as sea water and the like,may, however, be used. In instances where it is desired to drill withsalt water muds, such as through heaving shale, even water saturatedwith salt may be used.

The Irish moss may be used in bleached or unbleached and in whole,ground, shredded or powdered form. Since the various forms aresubstantially the same in their efiectiveness, the

ground unbleached variety is preferred from the standpoint of economyand ease of dispersion.

A drilling fluid containing Irish moss shows improved plasteringproperties, including resistance to flocculation of the suspendedcolloids by salt contaminations or by increased temperature, asillustrated in the tables given hereinbelow. To samples of a basedrilling fluid or mud, composed of a Ventura clay drilling fluid made upto a. weight of about 79 lbs. per cu. ft., additions of various agentswere made to show by comparison the improved properties of drilling mudsprepared according to the present invention. Low values for the loss ofwater through a mud sheath formed at 100 lbs. pressure on a filter withan area of about 17.5 sq. cm. have been used as a measure of desirableplastering properties. The concentrations of salt are given in percentsaturation of the water content of the drilling fluid and viscosities,when given, are in centipoises as measured in a Stiirmer viscosimeter.

Table I illustrates the efiect of increasing amounts of saltcontamination on quebrachosoda treated mud with and without Irish moss.

Table II shows the effect of temperature on treated muds and theimprovement obtained by the addition of Irish moss.

Table II Water loss at- Test Addition to quebracho-soda treated base No.mud having salt saturation ll None 62. 2 95.0 12 0.54% Irish moss 3. 313.3

Table III shows the relative water losses of variously-treated mudscontaining Irish moss and sodium alginate, comparative tests having beenrun before and after letting the drilling fluid stand for about eightdays at about F.

Table III C. 0. water loss 'lllfast Addition to base mud Before AfterNone 35. 2 36. 7 0.3% Irish moss 11.9 16. 4 0.3% Irishmoss+qucbracho-soda 10.6 5. 2 0.3% Irish moss+pyrophospl1ate 9. 7 12. 70.3% sodium alginate 4. 0 52. 4 0.3% sodium alginate+quebracho soda. 5.0 15. 4 0.3% sodium algiuate+pyroph0spl1ate 4. 0 25.8

Table III shows that Irish moss alone (test 22) is greatly superior tosodium alginate alone (test 25) after standing for several days, theincrease in water loss for Irish moss-treated mud being only 38% ascompared to 1210% for alginate-treated mud. A quebracho-soda treated mudcontaining alginate (test 26) shows an increase in water loss of 208%while a like treated mud containing Irish moss (test 23) shows adecrease in water loss of 51%.

Bali.

Table IV Chemical treatment quebrachooda Addition to base None 25223 mudcontaining salt Test N 0.

Viacos- Viscosity Water loss Water Water loss loss None 0.3% Irish moss0.3% calcium alginate. 0.3% Na algmate.

It may be seen from Table IV above that the treating agents, such asquebracho-soda and pyrophosphate, which are commonly known as viscosityreducers, do not cause a substantial reduction in the viscosity of thedrilling fluids but in some cases, such as in particular with calciumalginate (test 33), cause a great increase. It may be noted also thatthe water loss with untreated mud containing calcium alginate (test 33)is slightly greater than that for untreated mud alone (test 31), whilethe addition'of Irish moss (test 32) to untreated mud causes a greatdecrease in the water loss.

Thus, it may be seen from the above tables that the plasteringproperties of straight drilling fluids or muds are markedly improved bythe addition of small amounts of Irish moss with or without treatmentwith a compound of the class known as viscosity reducers, such asquebrachosoda. These tables further illustrate that formation saltsflocculate the colloidal particles in ordinary untreated drillingfluids, and consequently prevent the development of a mud structuresuitable for forming an impermeable mud sheath on the walls of theborehole. fluids treated according to the However, drilling presentinvention are not appreciably affected by salt contamination; that is,the treated fluids are able to form the desirable thin, impermeable mudsheath on the well walls due to a quasi-protective colloidal. action ofthe Irish moss permitting the formation of a weak gel which isadvantageous in promoting a. thixotropic structure and subsequentformation of the desired mud sheath. This protective action of the Irishmoss is likewise not greatly affected by high temperatures which tend toflocculate the colloidal particles or by standing for some time and, infact, in conjunction with materials like quebracho-soda the action ofIrish moss is improved with time.

The protective action of the Irish moss is not due to containedalginates since the mucilaginous substance obtained from Irish moss,according to the usual alginate extraction methods, diflers from alginin that it is not precipitated by neutralization with acid or by calciumsalts.

We claim as our invention: I

1. In a process for drilling wells, the step of introducing andcirculating in the drill hole a drilling fluid containing Irish moss inaqueous dispersion.

2. In a process for drilling a borehole through formations allowing aninflow of brine into the borehole, the step of circulating in theborehole a drilling fluid containing Irish moss dispersed therein.

3. In a process for drilling wells, the step of circulating in the drillhole a drilling fluid containing Irish moss dispersed therein, an alkalihydroxide and a water-soluble salt of an organic material of feeblyacidic properties.

4. In a process for drilling a borehole through heaving shaleformations, the step of circulating in the borehole a drilling fluidcontaining a high concentration of salt dissolved in the aqueous mediumand Irish moss dispersed there 5. A drilling fluid comprising acolloidal material and Irish moss dispersed in an aqueous medium, havinga high concentration of salt dissolved thterein.-

6. In the process of drilling a borehole through formations having atemperature of about F., the step of preventing temperature flocculationby circulating in the borehole a drilling fluid containing Irish mossdispersed therein.

7. In a process for drilling wells, the steps of circulating in thedrill hole a drilling fluid con taining Irish moss dispersed therein,and a viscosity reducer selected from the group consisting of watersoluble alkali metal polyphosphate compounds.

8. In drilling oil and gas wells, the method of diminishing loss ofwater to the formation from a drilling fluid comprising a suspension ofsolid particles in water containing a substantial concentration of anelectrolyte, comprising the step of adding Irish moss to the drillingfluid.

JOHN W. FREELAND. HAROLD T. BYCK.

